How long are your shifts? Are they varied with day shifts or can you get into a routine with them? Are you alone on your night shifts? Can you vary them with periods of time when you can break routine?
DP used to do variable shifts, 3 x 7am - 7pm days, 3 x 7pm - 7am nights and 3 days off. Ultimately it gave him diabetes but he did have the freedom (eventually, when the night shifts were cut down from 2 to 1 staff) to do periodic physical workouts, reading, internet. Food wise, cook when you can (proper food), freeze it and make it easy for yourself to have healthy reheats. Sorry you are feeling so shit 